Optical objective



on 2.933.q 1a

April 19, 1960 l. C. SANDBACK OPTICAL OBJECTIVE Filed Sept. 20. 1957 SEARCH R06 ji/n for:

United States Patent OPTICAL OBJECTIVE Irving C. Sandback, Morton Grove, 11]., or to Bell iilzmllirliswell Company, Chicago, 111., a corporation of Application September 20, 1957, Serial No. 685,163

7 Claims. (Cl. 88-57) The invention relates particularly to optical objectives for photographic and projection purposes.

Petzval type objectives, comprising two widely spaced positive doublets, have been extensively used for projection purposes due to their relatively low cost and the large relative aperture attainable thereby. However, this design per se has a relatively high Petzval sum, which translated into image error means that it inherently has a large amount of curvature of field, so that the usable angle of coverage is relatively small. Adaptations of the basic Petzval design have been accomplished by interposing a relatively strong negative element adjacent the image or film plane, but this does not substantially increase the usable angular field.

The invention may be considered an improvement of the basic Petzval design, and has for its objects the provision of an objective which is corrected for spherical and chromatic aberration, coma, astigmatism, field curvature and distortion, and which has a usable angular field which is much greater than that of the conventional Petzval design without materially increasing the overall complexity of the optical system, while still maintaining a relatively high relative apereure and adequate clearance space between the rearmost component and the image or focal plane of the objective.

It is to be understood that the terms front and rear" as herein used refer to the ends of the objective respectively nearer the long and short conjugates thereof.

In the accompanying drawing forming a part hereof, Figures 1 and 2 respectively illustrate Examples 1 and 2 described herein of different objectives embodying the invention, and referring thereto each of the objectives comprises three air spaced components of which, beginning with the front of the objectives, the first component, designated at L is negative and is of meniscus form, and as shown comprises a single element, and the second and third components, respectively designated at L; and L are positive and comprise achromatized doublets, and the third component L; of Figure 2 additionally comprises a positive element closely spaced in front of the doublet thereof. The front and rear elements of the doublet of L, are respectively designated at 1 and 2 in Figures 1 and 2, the front and rear elements of the doublet of L; are respectively designated at 3 and 4 in Figures 1 and 2, and the additional positive element of L in Figure 2 is designated at 5.

Beginning with the front end of each objective R R etc. respectively designate the optical surfaces of the lens elements, t t etc. the axial thicknesses of the lens elements, s s etc. the axial separations of the components or lens elements, 6 designates the aperture stop of the objective, which is disposed at the front of the second component, and7 designates the image or focal plane.

The herein Examples 1 and 2 of the invention respectively conform with the following tables in which dimensions' are in terms of inches, and in which the indices of refraction for the D line and the Abbe dispersion numbers are respectively designated at n and v:

Example 1 [Equivelenttoeallength 1.0000. Beck tocallength.6020. Aperturef/LGJ R|=+1.0157 L1 tr= .4368 1|a= l.5704' v=48.1

sr==1.1959 Ra=+2.4600

ta= .2468 7ld=1.620 fl=60.0 La R4=- .7689

ts= .0985 fla=1.720 v=29.2 R =-1.3085

n=- .7161 Rs=+ .8779

l4= .2052 na=-l.517 64.5 In R1= .7631

ls= .0609 na=l.720 v=29.2 Rs=2.6125

Example 2 [Equivalent focal length 1.0000. Back focal length .621. Aperture 171.4.

R =+1.6793 L1 t1= .440 1la=1.620 v=60.0

tz=' .370 1la=1.617 D=55.0 In R4=1.0515

t;=- .120 na=1.720 12:29.2 Rs=2.22l2

sa= .8712 Rs=+l.6664

t4= .225 na=1.620 v=60.0 R1=+6.6666

83 .0075 In Ra=+ .8622

ts= .285 1|4=L589 v=61.0 Els -1.2022

to= .075 1l4=l.720 v=29.2 Rm=+1.4110

It will be observed that the objective of the invention has a relatively long back focal length, it exceeding onehalf of the equivalent focal length of the objective, and the objective has the following characteristics:

The distribution of power over the three components L L and L complies with the separations of the components comply with where f f and f are the focal lengths of the three components, and F is the equivalent focal length of the objective, the negative meniscus first component L complies with and the third component L complies with more particularly to balance the coma adequately.

Referring to Example 2, the additional positive element 5 of the third component L closely spaced in front of the doublet 3-4 thereof, substantially reduces the higher order spherical aberration, thereby enabling the relative aperture to be increased to f/ 1.4, and it is within the scope of the invention to compound one or more of the other components for better correction of the higher order aberration.

Since different embodiments of the invention can be made without departing from the spirit and scope thereof, it is intended that all matter shown in the accompanying drawing and described hereinabove shall be interpreted as illustrative and not in a limiting sense.

Wthat is claimed as new is:

1. An optical objective comprising three air spaced components of which, beginning at the front end of the objective, the first component is negative and of meniscus form and the second and third components are positive and comprise achromatized doublets, and further characterized in that the distribution of power over said components complies with the separations of said components comply with said first component complies with 7 .4 .6 and said second component complies with I?3 .7 R5 2.0 where f f and f are the focal lengths respectively of said first, second and third components, F is the equivalent focal length of the objective, and s; are the separations respectively of said first and second and of said second and third components, R and R are respectively the radii of the front and rear surfaces of said first component, and R and R are respectively the radii of the front and rear surfaces of said second component.

2. An optical objective as defined in claim 1 and further characterized in that the back focal length of the objective exceeds one half of the equivalent focal length thereof.

3. An optical objective as defined in claim 1 and further characterized in that said third component additionall comprises a positive element closely spaced in front of the doublet thereof.

4. An optical objective as defined in claim 1 and further characterized in that said first, second and third components comply with .8F R 2.0F .4F R- .9F 1.8F R 2.7F +l.0F R +2.5F .6F R 1.5F -2.2F -R, +2.9F

and said third component complies with -.5 +1.5 8 where R; and R are the radii respectively of the front and rear surfaces of said first component, R and R, are the radii respectively of the front and rear surfaces-of said second component, and R, and R are the radii respectively of the front and rear surfaces respectively of said third component.

5. An optical objective as defined in claim 4 and further characterized in that the back focal length of the objec tives exceeds one half of the equivalent focal length thereof.

6. An optical objective comprising three air spaced comments of which, beginning with the front end of the objective, the first component is negative and of meniscus form and the second and third components are positive and comprise achromatized doublets, and further characterized in that said objective complies substantially with the following table in which the dimensions are in terms of inches, and beginning with the front end of the objective L to L designate the components, R to R the radii of the surfaces, t to t the axial thicknesses, s and s, the axial separations, n the refractive indices for the D line, and v the Abbe dispersion numbers:

components of which, beginning at the front end of the objective, the first component is negative and of meniscus formand the se'cond and third components are positive and comprise aciiiomatized doublets and the third component additionally comprises a sitive element closely spacpd in front of the doublet thereof, aifd further characterized in that sat BBjEtiVWifiplies substantially with the following table in which the dimensions are in terms of inches, and beginning with the front end of the objective L to L designate the components R to R the radii of the surfaces, t to i the axial thicknesses, s to s the axial separations, n the refractive indices for the D line, and v the Abbe dispersion numbers:

R.=+1.0793 L, n= .440 7ld=1-620 u=60.0

i,= .370 7Zd=1.617 0=55.0 L1 Rt=1.0515

t== .120 7Zd=1.720 v=29.2 R5=2.2212

sz= .8712 R0=+1.6664

t .225 fla=1.620 v=60.0 R1=+6.6666 sa= .0075 La Rs=+ .8622

.285 nd=1-589 v=61.0 R: 1.2022

tt= .075 na=1.720 v=29.2 R|o=+1.41l0

References Cited in the file of this patent UNITED STATES PATENTS 1,863,099 Bowen June 14, 1932 2,076,190 Wood Apr. 6, 1937 2,384,624 Kingslake et a1. Sept. 11, 1945 2,594,020 Hopkins et al Apr. 22, 1952 2,594,021 Hopkins et al Apr. 22, 1952 FOREIGN PATENTS 891,469 Germany Sept. 28, 1953 

